The present invention relates to a device for measuring and displaying laser outputs for a laser knife.
In almost all conventional laser knives, a power meter is provided in the housing of the laser oscillator of the device so that the laser output at the emergence port of the laser oscillator is measured by the power meter and is displayed by a meter on the panel of the laser source housing.
In general, a laser beam is introduced to the end of the operating section of a laser knife, namely, the handpiece, through a flexible optical conduction device called a manipulator whereby the laser beam is applied as a minute optical spot to the part of the body to be operated upon. In general, seven reflecting mirrors are provided in the articulation section of a manipulator and a focusing lens is provided in the handpiece. The power of the laser beam is attenuated by the these reflecting mirrors in accordance with their reflection factors and the focusing lens in accordance with its transmission factor. For instance in the case where the reflection factor and the transmission factor are both 97%, a laser power of 30 W at the emergence port of the laser oscillator is reduced to 23.5 W at the emergence terminal of the handpiece.
The laser knife operator should confirm the laser power before the surgical operation. The laser power which should be confirmed by the operator is not that at the emergence port of the laser oscillator but that at the emergence port of the manipulator. It is true that the laser knife is so designed that the operator can readily increase or decrease the laser power and the laser irradiation time according to the conditions of the body part to be operated; however, in a conventional laser power measuring technique, it is impossible for the operator to directly know the irradiation laser power.
A drawback accompanying the conventional laser power measuring method is that the reflection factors of the above-described reflecting mirrors are not uniform and moreover they change with time. Accordingly, the ratio of the laser power at the emergence port of the laser oscillator to the laser power at the emergence port of the manipulator is not always constant. The reason why the reflection factors change with time is that dust falling on the reflecting mirrors becomes firmly attached to the vacuum-evaporated films on the mirror surfaces by the laser beams thereby decreasing their reflection factors. On the other hand, the transmission factor of the focusing lens is also reduced for the same reason and also due to contamination by carbonized tissue produced during operations.
In addition, it is well known in the art that, as a laser oscillation mode can be changed from a single mode to a multi-mode by thermal or mechanical deformation of the laser oscillator, the ratio of the laser power at the output port of the laser oscillator to the laser power at the output port of the manipulator has a tendency to change.
Laser knife manufacturer commonly use commercially available portable laser power meters to measure the laser power at the end of the manipulator during manufacture and test. However, it is not suitable for technical and security reasons for the user to perform such measurements during a surgical operation.